Dental implant technology is a mature technology that is becoming increasingly affordable and popular. This is a second line of defense apart from the root canal procedure with a cemented crown.
The common titanium alloy dental implant system consists of an implant that goes into the jaw bone, a titanium alloy abutment, a titanium alloy abutment screw, and a zirconia cemented crown or screw-retained cemented crown.
The success of a dental implant depends on many factors. Some patients do not have sufficient bone after extraction of the tooth, and therefore will require grafting, a type of artificial bone matrix that can be fused with the jaw bone. Pilot tap drills are used to prepare for the implant installation. The general design of an implant has a threaded outside profile and internal threads for mating with the abutment screw. Some implant designs can achieve thread forming and therefore no tapping is required when preparing the drilled cavity for the implant installation. The implant will be screwed and secured into the jaw bone at or 1 millimeter (mm) to 2 mm below the crest of the bone.
A secure implant primary mechanical stability is critical for the success of the implant integration. Usually the patient has to wait for a few months to ensure a successful osseointegration, a biological bone growth process around the threaded implant. This is often referred to as the secondary stability. The implant with good secondary stability can withstand the occlusal loads of mastication on the crowned abutment.
For the cemented type crown, the abutment will be secured to the implant by the abutment screw followed by the crown cementation. The bonding of the cemented crown to the abutment with resin cement is generally non-permanent and therefore allows the crown to be removed from the abutment with the use of a special tool. The abutment screw will be screwed down at a prescribed torque value from the dental implant manufacturer. For the screw-retained cemented type crown, the crown is permanently fused onto the abutment. The screw-retained cemented crown has a small through hole that accepts the abutment screw into the abutment and secures the abutment to the implant. A small filling procedure will be administered to cover the small circular hole for functional and aesthetics purposes.
One of the major issues of the current implant system is that the abutment screw will become loose over time due to cyclic occlusal loads on the cemented crown or screw-retained cemented crown. The occlusal load has one vertical component and one lateral force component. The abutment screw will exhibit a normal fatigue failure life due to cyclic vertical loads on the crown. The cyclic lateral loads on the crown will cause a joint slip at the contact interface between the abutment screw and the abutment. This joint slip effect will reduce the prescribed torque on the abutment screw and cause it to self-loosen. Usually, at the very early stage of abutment screw self-loosening, a slight rotational movement of the crown is noticeable. The patient should then seek a dental appointment to re-torque the abutment screw. A delayed response will lead to further self-loosening of the abutment screw, bending loads, micro-crack propagation, and subsequent failing due to fatigue.
Another major issue is the retrieval of the broken abutment screw remnant inside of the implant. This is truly a well-known challenging and time consuming issue in the dental implant dentistry. Many dentists have used special tools or come up with their own custom tools in order to tackle this problem. As discussed in the previous section, the abutment screw will become loose and fail at some point in time due to fatigue. The location of breakage or fracture along the abutment screw will dictate the level of difficulty for accessibility and retrievability. Some abutment screws fail and sheer just below the screw head, but the remaining portion is visible and tool-accessible. Other abutment screws fail anywhere along the threaded length with limited visibility and tool accessibility. In addition, there is another risk of damaging the implant internal threads and making the implant non-usable when operating the special tools to retrieve the broken abutment screw.
Accordingly, a need exists for a new dental implant system to resolve the two major foregoing issues.